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Phenocryst

About: Phenocryst is a research topic. Over the lifetime, 4132 publications have been published within this topic receiving 158441 citations.


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TL;DR: In this paper, the authors measured the segregation pressures of primary basaltic magmas of NW Rota-1 volcano (primary COB and plagioclase^olivine basalt (POB) in the Mariana arc.
Abstract: Primitive basalts are rarely found in arcs.The active NWRota-1 volcano in the Mariana arc has erupted near-primitive lavas, which we have sampled with ROV Hyper-Dolphin (HPD). Samples from the summit (HPD480) and eastern flank (HPD488) include 17 magnesian basalts (51^52 wt % SiO2) with 7·5^9·5 wt % MgO and Mg-number of 61^67, indicating little fractionation. Olivine phenocrysts are as magnesian as Fo93 and contain 0·4 wt % NiO; the Cr/(CrþAl) values of spinels are mostly 0·5^0·8, indicating equilibrium with depleted mantle.There are three petrographic groups, based on phenocryst populations: (1) cpx^olivine basalt (COB); (2) plagioclase^olivine basalt (POB); (3) porphyritic basalt. Zr/Y and Nb/Yb are higher in POB (3·1^3·2 and 1·2^1·5, respectively) than in COB (Zr/Y1⁄4 2·8^3·0 and Nb/ Yb1⁄4 0·7^0·9), suggesting that POB formed from lower degrees of mantle melting, or that the COB mantle source was more depleted. On the other hand, COB have Ba/Nb (70^80) and Th/Nb (0·4^ 0·5) that are higher than for POB (Ba/Nb1⁄4 30^35 and Th/ Nb1⁄4 0·1^0·2), and also have steeper light rare earth element (LREE)-enriched patterns. Moreover, COB have enriched Sr/Sr and Nd/Nd, and higher Pb isotope values, suggesting that COB has a greater subduction component than POB. Hf/Hf between COB and POB are similar and Hf behavior in COB and POB is similar to that of Zr,Yand HREE, suggesting that Hf is not included in the subduction component, which produced the differences between COB and POB.The calculated primary basaltic magmas of NW Rota-1 volcano (primary COB and POB magmas) indicate segregation pressures of 2^1·5 GPa (equivalent to 65^50 km depth).These magmas formed by 24^18% melting of mantle peridotite having Mg-number 89·5. Diapiric ascent of hydrous peridotite mixed heterogeneously with sediment melts may be responsible for the NW Rota-1 basalts. These two basalt magma types are similar to those found at Sumisu andTorishima volcanoes in the Izu^Bonin arc, with COB representing wetter and POB representing drier magmas, where subduction zone-derived melt components are coupled with the water contents.

57 citations

Journal ArticleDOI
TL;DR: The Breccia Museo Member (BMM) was formed by an explosive eruption that occurred in the SW sector of Campi Flegrei about 20 ka ago as discussed by the authors.

57 citations

Journal ArticleDOI
TL;DR: The authors analyzed whole rocks, minerals, and silicate melt inclusions from the co-genetic, ore-contemporaneous volcanic package (∼38 Ma) and showed that the latites were Cu rich, with Cu concentrations in the silicates melt reaching up to 300-400 ppm at about 60 wt% SiO2.

57 citations

Journal ArticleDOI
TL;DR: In this article, major element and volatile concentration analyses in melt and gas inclusions from two recent picrite eruptions (February 2005 and December 2005) at Piton de la Fournaise volcano (La Reunion Island, Indian Ocean).
Abstract: We present major element and volatile concentration analyses in melt and gas inclusions from two recent picrite eruptions (February 2005 and December 2005) at Piton de la Fournaise volcano (La Reunion Island, Indian Ocean). Combined with literature data, our new data show that the large variability of major element compositions in Piton de la Fournaise lavas may be explained by three depth-dependent differentiation stages of a single transitional parental magma (9–11 wt% MgO; 0.5–0.8 wt% K2O, and 10–12 wt% CaO). The deepest differentiation (>7.5 km) is controlled by the fractional crystallization of clinopyroxene + plagioclase and yields gabbros and basalts enriched in K and depleted in Ca relative to the parental magma. In a shallower storage zone (<2.5 km), differentiation of the transitional parental magma is dominated by the fractionation/accumulation of Fo83–85 olivine phenocrysts, yielding Mg-poor basalts at the top of the reservoir and picrites at the base. In cooling dykes and subsurface pockets (<0.6 km), Mg-poor basalts may themselves evolve into more differentiated melts by clinopyroxene + plagioclase fractionation. The incorporation of dunitic xenocrysts or other xenoliths is not necessary to explain the major element chemical diversity of the volcano. The same superposition of differentiation mechanisms may occur at similar depths in other shield volcanoes.

57 citations

01 Jan 1990
TL;DR: In this article, phase equilibrium experiments on Serocki lava ALV-1690-20 have been carried out at 1 atm and 8 kbar, and the results provide a framework for quantifying the effects of fractional crystallization on the abundant parental group MORB near the Kane Fracture Zone (KFZ), Mid-Atlantic Ridge.
Abstract: Phase equilibrium experiments on Serocki lava ALV-1690-20 have been carried out at 1 atm and 8 kbar. The results provide a framework for quantifying the effects of fractional crystallization on the abundant parental group MORB near the Kane Fracture Zone (KFZ), Mid-Atlantic Ridge. The least-evolved parental group MORBs, as exemplified by Serocki lava ALV-1690-20, are not in equilibrium with a mantle peridotite residue in the plagioclase stability field. Multiply saturated liquids from 8 kbar experiments have pigeonite as their low-Ca pyroxene, and have low Mg#, high Na20 and high Ti02 compared to the parental group lavas. The variation in composition between glass and whole rock from Serocki volcano can be accounted for by plagioclase accumulation. Elevated pressure fractional crystallization of olivine, plagioclase, and augite at 5-6 kbar can account for compositional variation in spatially related lavas from the vicinity of Serocki volcano. Plagioclase phenocrysts or xenocrysts, which are abundant in Serocki lavas, did not crystallize from a liquid of Serocki lava composition at any pressure under anhydrous conditions. These exotic An-rich plagioclase (An84) may have crystallized at elevated pressure from a precursor magma with higher MgO and CaO and lower Na20 contents, or may record a mixing event with a distinctively low-Na20 magma type.

57 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202399
2022142
2021105
2020100
2019103
2018109